The present invention relates to a polishing composition to be used for polishing a semiconductor device having a tungsten film and an insulating film, to be used for e.g. substrates for semiconductors, photomasks and various memory hard disks, particularly to a polishing composition useful for planarization of the surface of device wafers in e.g. semiconductor industry, and a polishing method employing such a composition.
More particularly, the present invention relates to a polishing composition which is capable of forming an excellent surface having excellent flatness and no light damage by polishing and not stained with impurities such as iron ions in the polishing of semiconductor devices to which so-called chemical mechanical polishing (hereinafter referred to as xe2x80x9cCMPxe2x80x9d) technology is applied, in the processing of device wafers for the production of semiconductor devices having at least a tungsten film and an insulating film, and a polishing method employing such a composition.
Progress of computer products has been remarkable in recent years, and parts to be used for such products, such as ULSI devices, have been developed for high integration and high speed, year after year. Along with such progress, the design rule for semiconductor devices has been progressively refined year after year, the depth of focus in a process for producing devices tends to be shallow, and planarization required for the pattern-forming surface tends to be increasingly severe.
Further, along with refinement and high integration of devices, wirings on the devices have become increasingly complex, and accordingly, it has been required to stack multilayered wirings on a silicon surface. In a process of stacking the respective layers, it has now become important to maintain flatness of each layer in order to form a wiring of its upper layer with good precision. CMP is used as the most effective means for this planarization. CMP may be generally classified into two types i.e. a method of polishing for planarization of an insulating film of silicon dioxide, silicon nitride, monofluoro silicon oxide or the like, and a method of polishing for planarization of a metal film of tungsten, copper, aluminum, an alloy thereof or other metal.
Among such metal films, a tungsten film is used for a contact wiring of a relatively low layer, as tungsten is excellent in heat resistance and stability. For CMP against tungsten, a method has been employed in many cases wherein a tungsten film is polished and removed with a polishing composition comprising abrasive grains such as silica or alumina, an oxidizing agent such as hydrogen peroxide and a catalyst such as iron ions, and polishing is terminated when the insulating layer appears.
However, when a conventional polishing composition is employed for polishing, due to the presence of impurities such as iron ions, there has been a problem such that light damage is observed on the device surface after polishing, or iron ions are likely to remain attached on a wafer after polishing and deteriorate the characteristics of the semiconductor device. Further, the surface after polishing may have irregularities caused by the difference between the stock removal rate of the tungsten film and the stock removal rate of the insulating layer by the polishing composition, which tends to further worsen the yield of the device.
The present invention has been made to effectively solve the above problems. Namely, it is an object of the present invention to provide a polishing composition which is capable of forming an excellent surface having excellent flatness and no light damage by polishing and not stained with impurities such as iron ions, in the polishing of a semiconductor device having at least a tungsten film and an insulating film.
Further, it is another object of the present invention to provide a polishing method which comprises carrying out the finish polishing by means of the polishing composition of the present invention, after polishing and removing the majority of a tungsten film, in the polishing of a semiconductor device having at least a tungsten film and an insulating film, whereby an excellent surface having excellent flatness and no light damage by polishing, can be formed and staining with impurities such as iron ions, can be prevented.
The polishing composition of the present invention is one for polishing a semiconductor device having at least a tungsten film and an insulating film, which comprises the following components (a) to (d):
(a) silicon dioxide,
(b) periodic acid,
(c) at least one pH controlling agent selected from the group consisting of ammonia, potassium hydroxide, sodium hydroxide, ammonium periodate, potassium periodate and sodium periodate, and
(d) water.
The polishing method of the present invention is such that in a process for polishing a semiconductor device having at least a tungsten film and an insulating film, it comprises polishing the tungsten film and the insulating film simultaneously with a polishing composition which comprises the following components (a) to (d):
(a) silicon dioxide,
(b) periodic acid,
(c) at least one pH controlling agent selected from the group consisting of ammonia, potassium hydroxide, sodium hydroxide, ammonium periodate, potassium periodate and sodium periodate, and
(d) water.
Further, the method for polishing a semiconductor device according to the present invention, is such that in a polishing process for production of a semiconductor device having at least a tungsten film and an insulating film, it comprises carrying out the finish polishing with the above-mentioned polishing composition, after removing the majority of the tungsten film.
According to the present invention, in the polishing process for the production of a semiconductor device having at least a tungsten film and an insulating film, the tungsten film and the insulating film can be polished while maintaining substantially the same stock removal rates in the finish polishing step after removing excess tungsten by polishing, and as a result, good flatness can be realized, and a surface having no light damage by polishing and not stained with impurities such as iron ions, can be obtained.